The present disclosure relates to voltage controlled oscillators, and in particular, to a multimode voltage controlled oscillator.
Many electronic systems require some kind of signal to control timing of the circuits and functions of the system. One common circuit for generating a timing signal is a voltage controlled oscillator (VCO). VCOs typically receive an input voltage and produce a periodic signal having a frequency determined by the input voltage.
One common VCO architecture uses differential cross coupled NMOS transistors with drains connected across a voltage controlled inductor/capacitor (LC) tank circuit. Such circuits are known to operate at very high frequencies with large voltage swings, but they can consume a great deal of power. Another common VCO architecture uses cross coupled CMOS devices (PMOS and NMOS transistors) across an LC tank. CMOS VCOs consume less power, but may have more phase noise and a lower voltage swing than NMOS VCOs.
A multimode VCO may switch between an NMOS mode and CMOS mode. However, the performance of such an architecture may suffer if large capacitances in the circuit interfere with the capacitance of the LC tank, for example. Additionally, voltage swings in NMOS mode should not be impacted by circuitry that is only used in CMOS mode. Further, switching circuits to reconfigure the VCO between modes may degrade performance by reducing tuning range or degrading phase noise, for example.
Embodiments described herein disclose a multimode VCO that may overcome these and other challenges.